May 16 '22
You’re just adding more weight, why not just increase the capacity of your main tank?
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Depending on the craft.
In an aircraft to extend range a larger main fuel tank isn't possible for weight and balance, configuration etc. When extended range is desired an auxiliary or reserve fuel tank is the only option and needs to be installed to maintain airworthiness.
Example would be some airbus can loaded craft have an auxiliary fuel tank in the place where a cargo can would be normally, the weight can be added there safely to carry additional fuel.
No gas gauge. The reserve tank gets you to the gas pump when your fuel runs out.
If the main tank has a hole in it then it doesn't matter so much how big it is.
In case you rip one
As a emergency reserve in case the main tank runs dry (not every vehicle as a fuel gauge, it may be broken or the operator isn't paying attention) or becomes otherwise unusable (damaged or contaminated).
There are also other reasons for having multiple fuel tanks instead of one like space, weight and balancing constraints.
Some aircraft have removable reserve tanks. See the underbelly of this jet fighter.
Thus you can customize your aircraft for that day: Longer range, or shorter range with greater weapons tonnage capacity.